Lake Heviz is 47,500 square meters and it’s estimated to be about 22,000 years old. The water that erupts into the cave is also old. The thermal water is believed to be about 10,000 years old, where as the cold water is “only” 8,000 years old. The water emerges from a depth of about 1,000 to 2,500m / 1500 / 8000 feet. Every 83 hours the lake replenishes itself.